Soilborne plant pathogenic fungi and oomycetes cause severe economic losses in the agricultural and horticultural industries. For example, root and crown rot diseases caused by pathogens such as different Pythium spp. are a widespread and recurrent problem in plant production. As another example, Rhizoctonia solani is a major soilborne fungal phytopathogen, and is associated with diseases such as damping-off, root rot, and leaf and stem rot in many plant species, including greenhouse crops. R. solani is also associated with brown patch in creeping bentgrass and various other turfgrasses of high commercial value. Species of Alternaria and Fusarium are associated with diseases such as early blight of tomato and Fusarium wilt of numerous fruit and vegetable crops.
In light of actual and potential environmental and health hazards associated with pesticide use, chemical fungicide use may be restricted. And, certified organic growers may not use synthetic chemicals for pest management. As a result, growers have sought alternative approaches to disease control. These alternative approaches include the use of biological agents and disease-suppressive growing media. The use of biologically active agents in the control of plant pests and diseases has become especially important. Despite the recent commercialization of several types of microbial biocontrol agents, questions still remain about the ability of these agents to provide consistent and reliable control against pathogens.